1. Field of the Invention
This invention relates to heat pipes and in particular to a method and means for inhibiting corrosion within a heat pipe. The method and means is advantageously adapted for use with heat pipes such as used in domestic furnaces.
2. Description of the Background Art
In one well-known form of heat pipe, water is provided in a sealed enclosure which defines, at one end, an evaporator portion and at the opposite end, a condenser portion. When used in conventional domestic furnace, the evaporator portion is heated by flue gases and the condenser portion is cooled by the circulating air to be heated. Such heat pipes are advantageously adapted for use in furnaces as they are capable of transferring large amounts of heat in a small amount of space. However, a serious problem arises in that while such heat pipes have conventionally been formed of stainless steel, the water preferentially used as the heat transfer medium tends to corrode the pipe at the elevated temperatures normally involved in the operation thereof as a heat pipe in a furnace. The corrosion produces hydrogen, which when present in a sufficient amount, interferes with the efficiency and operating parameters of the heat pipe. Illustratively in a furnace, it is desirable to operate the heat pipe at temperatures of over 300.degree. F. and up to approximately 500.degree. F., with an average temperature of operation being approximately 425.degree. F.
Another problem is the potential freezing of the water in the heat pipe and bursting of the heat pipe when the unit is installed where the ambient temperature may drop below 32.degree. F. at times.
A still further problem arises in the chemical reaction involved when the water reacts with the iron of the heat pipe inner surface portion to form successively FeO, Fe.sub.3 O.sub.4, and Fe.sub.2 O.sub.3, in each of which formations hydrogen is evolved. The evolution of the hydrogen interferes with efficient condensing action in the heat pipe by blocking the path to the upper part of the condenser and, thus, the overall efficiency of the furnace is reduced.
One attempted solution to the problem of preventing corrosion caused by subjection of metals to aqueous liquids is to dissolve therein alkali metal chromates. One such method is illustrated in U.S. Pat. No. 1,405,320 of Arthur Z. Pedersen, wherein a mixture of calcium chloride and potassium chromate is dissolved in an antifreeze mixture.
In U.S. Pat. No. 2,411,676, Lloyd M. Burghart discloses a corrosion inhibiting composition and method for aqueous antifreeze solutions, such as used in the cooling systems of internal combustion engines. Burghart teaches the use of an alkali metal borate and a compound of the group consisting of alkali metal chromates and dichromates, together with a compound of the group consisting of alkali metal orthosilicates, alkali metal silico-fluorides, and aluminum alkali metal silico-fluorides.
Arthur L. Jacoby discloses, in U.S. Pat. No. 2,582,129, a corrosion inhibiting composition comprising an aqueous solution of sodium chromate and sodium nitrate.
John Nelson Wanklyn et al, in U.S. Pat. No. 3,171,789, teach the method of inhibiting corrosion by introducing boric acid into steam.
While a number of attempts have been made to solve the vexatious problem of corrosion of metal, such as ferrous metals forming heat pipes and the like, none has proven completely satisfactory.